The invention concerns a method for the production of hydrocarbon resins. Hydrocarbon resins are used, for example, as binding agents for printing colors, as lacquer components, as impregnation and adhering agents for paper preparation or for modification of plastic masses. For this reason, these resins should as a rule display a light color, possess a high softening point, and dissolve easily in aromatic and aliphatic solvents. Moreover, they require a good compatibility with other lacquer raw materials, terpenes and rubbers.
It is already known to produce hydrocarbon resins through cationic polymerization of aliphatic or cyclic monoor di-olefins or of aromatics, which contain a reactive double bond in the side chain or in an adjacent ring. For the cationic polymerization there will be used, in particular, the olefin mixture obtained by the cracking of crude oil (so-called C.sub.4 - or C.sub.5 -cuts) or higher boiling pyrolytic oils, which are rich in unsaturated, preponderantly aromatic compounds.
It is furthermore known to carry out the cationic polymerization in the presence of Friedel-Crafts catalysts, for example AlCl.sub.3, SnCl.sub.4 or BF.sub.3, which have been activated through addition of an acid, an alcohol or an ether. If the mixture that is to be polymerized displays a high content of unsaturated compounds, the polymerization will be carried out in the presence of an inert solvent, for example toluene or xylene, chlorbenzene or methylene chloride. The temperature for the polymerization in general lies between -40.degree. and +60.degree. C., preferably between -20.degree. and +40.degree. C.
It is moreover known (see Fuel 1979, vol. 58, pages 211-214) that with the pyrolysis of tetralin, in addition to small amounts of 2-methyl-indene, mainly styrene, indene and 1,2-dihydronaphthalene are formed. Herewith the pyrolysis will be accomplished above 725.degree. C. in the presence of nitrogen as carrier gas. For optimal progress the cracking reaction should first take place, however, between 750.degree. and 850.degree. C. At 775.degree. C. and a contact time of 0.5 seconds the reaction mixture contains for example 3.0% styrene, 5.0% indene, as well as 24.6% 1,2-dihydronaphthalene.